Risks to participants. Participants may experience side effects from clonidine such as sedation and are expected to experience brief, mild psychological stress and drug craving from the laboratory script procedures. Prior to leaving the session, participants will be assessed for the presence of continued drug effects. If participants are experiencing any stress or craving at the end of the session, they will undergo a 10-minute guided relaxation session, which will be repeated until feelings of stress or craving dissipate, before being released from the laboratory. Participants may be kept longer than the planned session length, up to and including staying overnight on the inpatient ward, because of continued side effects or elevated stress or craving. If the MRP deems it medically necessary, participants will be sent to JHBMC emergency department for further evaluation and treatment.